Non-volatile memories are capable of permanently retaining data contained therein, in the absence of external electric power. Exemplary of non-volatile memories are magnetic tapes, magnetic coil memories, bubble memories and semiconductor memories employing metal nitrite oxide silicon (MNOS) technoloy. Non-volatile memories are erasable by the action of electronic and, in some cases, radiant energy fields applied to elements in the memories. The non-volatile memories can hold a maximum amount of data, depending on the number of elementary cells included therein, which number defines the capacity of the memory. The capacity of a non-volatile memory limits the number of operations for which the memory can be used. When the amount of data stored in the memory reaches the memory capacity, the user of the memory has two options. In particular, he can stop using the memory and employ another memory having no data in it or he can consider erasing i.e., changing, the portion of the memory where changeable data are stored, to make that portion of the memory available for reuse.
In many applications, data stored in a non-volatile memory is of no further use after a significant number of additional operations have been performed on the memory. In such instances, it is far preferably to erase or change the contents of the memory, in contrast to obtaining a new memory. In memories that are mounted on credit cards, erasure of the memory is preferable to replacement. In the credit card application, however, it is imperative that changing the data stored in memory can only be performed with authorization from the credit card issuing agency. Otherwise, the credability of systems using the credit cards would be virtually destroyed. It is thus apparent that holders of credit cards containing electronic memories cannot be allowed to modify or erase any of the changeable data that might be stored therein.
It is, therefore, an object of the present invention to provide an apparatus for and method of enabling erasure of non-volatile memories only under certain conditions.
Another object of the invention is to provide an apparatus for and method of erasing non-volatile credit card memories in such a manner that the holder of a credit card cannot erase or change data in the memories without affecting the validity of the credit card.